Apparatus for and method of generating television signals



Aug. 4; 1942. A. G. JENSEN APPARATUS FOR AND METHOD OF GENERATINGTELEVISION SIGNAL S I Filed Feb 29, 1940 8 Sheets-Sheet l I By A. e.JENSEN APPARATUS FOR AND METHOD OF GENERATING TELEVISION SIGNALS FiledFeb. 29, 1940 a Sheets-Sheet 2 mQZOUum INVENTOR A. G. JENSEN ATTORNEK AAug. 4, 1942. A. G. JENSEN APPARATUS FOR AND METHOD OF GENERATINGTELEVISION SIGNALS Filed Feb; 29, 1940 s Sheets-Sheet s INVENTOR A.GJE/VSZ'N AT; ORA/5y g- 4, 1942- A. G. JENSEN 2,291,723 APPARATUS FORAND METHOD OF GENERATING TELEVISION SIGNALS Filed'Feb. 29, 1940 sSheets-Sheet 4 mum Tum 8w 3 wm nl INVENTOR A. G. JENSEN ATTORNEY Aug. 4,1942, A: G. JENSEN APPARATUS FOR AND METHOD OF GENERATING TELEVISIONSIGNALS Filed Feb. 29, 1940 8 Sheets-Sheet 5 INVENTOR AGJENSEN ATTO EV 8Sheets-Sheet 6 mOZOUum & 8 WM 3 o INVENTOR A G. JENSEN Bk ATTO MEI g-1942- A. G. JENSEN APPARATUS FOR AND METHOD OF GENERATING TELEVISIONSIGNALS Filed Feb. 29, 1940 FIG. 7

Aug. 4, 1942.

Filed Feb. 29, 1940 A. G. JENSEN APPARATUS FOR AND METHOD OF GENERATINGTELEVISION SIGNALS 8 Sheets-Sheet 7 INVENTOR A. 6. JENSEN BVW ATTORNEY4, 1942- A. G. JENSEN 2,291,723

APPARATUS FOR AND METHOD OF GENERATING TELEVISION SIGNALS Filed Feb. 29,1940 8 Sheets-Sheet 8 wOZOUuw w HH HH H HHHH. --H. --.fi.

lNl ENTOR AG. JENSEN BV 47m NE) Patented Aug. 4, 1942 APPARATUS FOR ANDMETHOD OF GENERATING TELEVISION SIGNALS Axel G. Jensen, Millburn, N. J.,assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y.,a corporation of New York Application February 29, 1940, Serial No.321,390

16 Claims.

This invention relates to signaling and particularly to apparatus forand a method of scanning motion picture film for generating televisionsignals.

An object of the invention is to provide improved apparatus for scanninga motion picture film for television transmission.

Another object of the invention is to provide novel means for generatingelectric waves having a desired wave form.

A standard motion picture film is exposed and projected at the rate of24 complete frames per second. In accordance with standards adopted byRadio Manufacturers Association, a field is scanned at the rate of 60field scans of 220 lines each per second with the lines of one fieldscan interlaced with those of the preceding or following field scan,thus resulting in 30 complete frame scannings of 441 lines each persecond. To produce a standard television signal when scanning standardmotion picture film, therefore, it is desirable to scan the odd filmframes of pictures twice, for example, and the even film frames threetimes, while the film is moved at the rate of 24 frames per second. Thusthe film is scanned at the rate of 60 field scans of 220 lines each persecond or 30 complete frame scannings of 441 lines, interlaced, persecond.

It has been proposed heretofore to scan standard motion picture film atthe rate of 60 field scans per second by scanning alternate film framesthree times and the remaining film frames twice. One method which hasbeen proposed requires that the film be moved forward intermittently atnon-uniform intervals. This method has the disadvantage that complexmechanical equipment is required to produce the non-uniform film motionand that the nonuniform intermittent film motion causes the film to wearrapidly. In accordance with another method which has been proposed forscanning alternate film frames three times and the remaining film framestwice, the film is moved continuously at a uniform rate. This priormethod requires the use of five prisms for splitting an image projectedfrom the film into five images and a rotating apertured shutter fordirecting light from the prisms one at a time in succession upon thecathode of a cathode ray tube in such manner that the successive imagesprojected upon the cathode occupy the same position thereon at thebeginning of each field scanning period.

The method of scanning standard motion picture film for televisiontransmission herein described has the advantage over prior art methodsthat the film is moved continuously at a uniform rate and that it doesnot require the use of optical image splitting apparatus or mechanicallymoving light directing apparatus.

In accordance with applicant's invention, a motion picture film isscanned by moving the film continuously at a constant rate and byapplying to a cathode ray scanning device a vertical deflecting fieldsuch that certain frames of the film are scanned an even plurality oftimes and other frames an odd plurality of times, the usual horizontaldeflecting field also being applied to the cathode ray scanning devicefor causing the film to be scanned along parallel lines substantiallyperpendicular to the direction of movement of the film. There is appliedto the cathode ray tube a vertical deflecting field substantially in theform of a saw-toothed wave of varying amplitude to cause the cathode raybeam to be deflected through different distances during differentperiods, respectively, occurring between successive return ornon-scanning deflections of the cathode ray beam. The vertical scanningdeflections may be such, for example, that twofield scans occur duringeach of two successive scanning deflections while a single.

field scan occurs during the next succeeding vertical deflection, thereturn deflections occurring between successive scanning deflectionsbeing of equal amplitude.

In accordance with a preferred specific embodiment of the inventionherein described for the purpose of illustration, a motion picture filmis moved continuously at the rate of 24 frames or pictures per secondthrough the film gate of a motion picture projector where the film is11- luminated and light from the film is projected upon the cathode of acathode ray image dissector tube to the horizontal deflecting coils ofwhich is applied a saw-toothed sweep current of 13,230 cycles persecond. The substantially saw-toothed wave which is applied to thevertical deflecting coils is produced by combining a plurality ofsaw-toothed waves, one cycle sawtooth edi wave and two 12 cyclesaw-toothed waves, the amplitude and phase relationship of the wavesbeing controlled so as to obtain a desired vertical sweep wave. Thesaw-toothed waves are generated under control of 60 cycle alternatingcurrent, or a harmonic thereof, which also controls the motor of themotion picture projector. The saw-toothed wave component or componentsof one frequency are characterized by a relatively slow increase inamplitude followed by an abrupt decrease in amplitude while a componentor components of the other frequency are characterized by a relativelyslow decrease in amplitude followed by an abrupt increase in amplitude.Preferably, the -blank lines or so-called "frame lines" occurringbetween pictures of the motion picture film are not scanned. To bringabout this result, the amplitude of the 60 cycle saw-toothed wavecomponent is reduced, thus causing the rate of change of amplitude withrespect to time of the resultant wave to be decreased during periodswhen picture portions are being scanned and increased during periodsbetween the scanning of successive pictures.

In accordance with an alternative embodiment of the invention, there isemployed a cathode ray device for illuminating the film an elementalarea at a time, light from the illuminated elemental areas beingreceived by a light sensitive image current generating device of theelectron multiplier type. for example. The deflection of the cathode raybeam is controlled in the same manner in which the deflection of thecathode ray beam of the image dissector tube is controlled.

The invention will now be described with reference to the accompanyingdrawings in which:

Fig. 1 is a diagram to which reference will be made in describing thescanning method and apparatus in accordance with the present invention;

Fig. 2 consists of curves to which reference will be made in describingthe invention;

Figs. 3 and 4, when Fig. 3 is placed above Fig. 4, constitute adiagrammatic view of motion picture film scanning apparatus inaccordance with the present invention;

Fig. 5 is a diagrammatic view of a modification of the portion of thefilm scanning apparatus shown to the right of line 5-5 as viewed in Fig.3; and

Figs. 6 to 8 are curves to which reference will be made in connectionwith the description of the scanning method and apparatus in accordancewith the invention.

In the upper portion'of Fig. 1 is shown a motion picture film III (theusual sound track being omitted for simplicity) in six successivepositions designated A to F, inclusive, the film beim in these positionsat the starting times of six successive field scanning periods. Thesuccessive frames of the film are designated by the Roman'numerals I,II, III, etc. The film is moved in the direction of the arrowscontinuously at the rate of 24 picture frames per second, for example.Each frame of the film consists of a picture portion II and a blankspace or frame line I! between that picture portion and the followingpicture portion. It will here be assumed that there is employed acathode ray device for illuminating the film an elemental area at atime, as disclosed in Fig. 5. At zero time the film is in position A andscanning of frame I is initiated at the elemental area a. in the lowerleft-hand corner of frame I. While the film is in motion, the cathoderay beam of the cathode ray scanning device is repeatedly deflectedhorizontally, that is, in a direction substantially perpendicular to thedirection of motion of the film, and rapidly returned to its startingposition between successive scanning deflections to cause the scanningof the film along successive transverse lines as the film is movedvertically, in the usual well-known manher. The cathode ray beam is alsosimultaneously deflected vertically in one direction parallel to thedirection of motion of the film and, at intervals, the beam is deflectedrapidly in the opposite direction to cause the light spot on the film tomove vertically in the direction opposite to the direction of motion ofthe film during each field scanning period, as will be described below.The horizontal deflections occur at the rate of 13,230 per second whichcorresponds to 441 lines in a complete frame scanning period of 3 secondor 220 lines in a field scanning period of second. Therefore, 220 lineselapse between the beginning of the field scanning period A and thebeginning of the succeeding field scanning period B, and the scanningduring the period B will begin with elemental area 0 in the middle of ascanning line as shown diagrammatically by the dot-dash line a|, thusresulting in the scanning lines of alternate field scans beinginterlaced.

In standard motion picture film the dimension of the frame lines I!along the length of the film is about 15 per cent of the length of theentire frame consisting of a picture portion II and a frame line l2,while in accordance with the R. M. A. standards there is a verticalblanking period between successive field scans of 7 per cent of thefield scanning period of ,4 second. In order to avoid waste oftransmission time, it is desirable to scan the picture portion only of aframe during 93 per cent of a field scanning period and allowing theremaining 7 per cent of the field scanning period between the time ofscanning the last scanned elemental area of one field scanning periodand the time of scanning the first elemental area in the succeedingfield scanning period.

For the sake of simplicity it will be assumed that as the scanning lightspot on the film moves along its vertical component in the directionopposite to the direction of motion of the film (from a to b, forexample) the cathode ray beam is also deflected vertically in thedirection opposite to the direction of motion of the film althoughactually the deflection of the cathode ray beam in one direction maycause the light spot to move in the opposite direction. In order thatthe field scannings may occur at the rate of field scans per second,while the film is moved at the rate of 24 frames per second, the oddframes, for example, are scanned twice and the even frames three times,that is, there are five field scans during second while the film movesthrough a distance equal to the lemgth of two frames. This will beapparent from Fig. 1. During 93 per cent of field scanning period A, thecathode ray beam is deflected vertically in a direction opposite to themotion of the film from a to b and during the remaining '1 per cent ofperiod A the beam is deflected vertically in the direction of motion ofthe film to c. During the vertical motion from b to c the beam is alsodeflected horizontally at the usual rate of 13,230 per second but forthe sake of simplicity this horizontal component is omitted in thedrawings. ,Point b does not necessarily fall in the middle of ahorizontal line but point 0 does, corresponding to a value of 220% linedeflections during the scanning of a complete picture frame plus frameinterval. During this field scanning period the film is moving fromposition A to position B. The picture portion of frame I is then scanneda-second time during 93 per cent of the second field scanning period 3due to the movement of the film and the deflection of the cathode raybeam from c to d in the direction opposite to the direction of movementof the film. During the remaining 7 per cent of this field seamingperiod, the beam is deflected in the same direction but at a higher ratefrom the last scanned elemental area d of frame I to the first scannedelemental area a of frame II. Similarly, the cathode ray beam isdeflected from c to j and returned to 9, deflected from g to h andreturned to i, and deflected from i to j for'scanning frame II threetimes. The deflection of the beam is then continued in the scanningdirection to in during the final '7 per cent of period E, the point Itbeing in horizontal alignment with point a, and the deflection is thencontinued to l, which is in horizontal alignment with b, during thefirst field scanning period of frame III.

The form of the voltage of current wave for vertically deflecting ascanning cathode ray beam in the manner indicated above is shown in thelower portion of Fig. 1, the scale of vertical deflection being inarbitrary units and the time scale being in seconds. This verticaldeflecting wave may be analyzed into a plurality of regular saw-toothedwave components, as shown in Fig. 2 and if desired, of course, a directcomponent may be added. Curve 2A is a duplicate of the wave shown inFig. 1 and curves 2B, 2C and 2D are the regular saw-toothed wavecomponents into which the wave 2A may be analyzed, the wave 23 being a60 cycle saw-toothed wave and waves 2C and 2D being 12 cycle saw-toothedwaves. In the 60 cycle wave, it will be noted, the amplitude risesrelatively slowly and then decreases abruptly, while in the 12 cyclewaves the amplitude rises abruptly and decreases relatively slowly. Thetwo 12 cycle waves are out of phase with respect to each other, the wave20 lagging wave 2D by cycle or t second.

Referring now to Figs. 3 and 4, the film II is driven continuously overthe film gate I5 at a constant rate of 24 frames per second, forexample, by any suitable mechanism including a synchronous motor I6which is energized from the 60 cycle power source I1. Light from sourceI8 is directed upon the portion of the film within the film by acondensing lens I9 and the projector lens 20 projects an image of theportion of the film within the film gate upon the cathode 2I of acathode ray tube 22. As indicated by the arrows, the image on thecathode is inverted with respect to the picture on the film. This filmmoving and projecting apparatus may be an ordinary motion pictureprojector from which the intermittent motion mechanism and light shutterhave been removed and having a film gate the heighth of which is about1% times the length of a motion picture frame in the direction of motionof the film.

The cathode ray tube 22 is a so-called image dissector, the imageprojected upon the light sensitive cathode 2I causing the emission ofelectrons from the elemental areas thereof in accordance with the lightactivation of the respective elemental areas. In addition to the cathode2| there are provided within the evacuated glass housing of tube 22, ananode 23 in the form of a metallic coating on the inner surface of thehousing and an electron multiplier 24 having multiplier plates I22,collector grid I23, anode I24 and a shield having a scanning aperture25. An electromotive force is applied between anode 23 and cathode 2Ithrough leads 26 and 21 from the circuit comprising battery 29, thepositive terminal of which is grounded, and a network 29 made up ofvoltage dividing resistors I25 and condensers I" as shown. Leads 90 fromcircuit 29 are connected to the multiplier segments I22 of the electronmultiplier 24 for aDDLVing accelerating potentials between the segmentsor multiplier plates and to the anode I24 and collector grid I23. Theelectrons emitted from cathode .2I are focussed so as to form anelectron image in the plane of the scanning aperture 25 by means of anaxial magnetic field set up due to the current from source 3| flowingthrough the coil 32 surrounding the glass envelope and extendingsubstantially the full length of the cathoderay tube. There are providedtwo pairs of deflecting cells, the horizontal or high frequencydeflecting coils 33 andthe vertical or low frequency deflecting coils94. The magnetic fields set up when these deflecting coils are suitablyenergized cause the beam of electrons emitted from cathode 2i andtherefore the electron image focussed in the plane of the scanningaperture 25 to be deflected along both horizontal and verticalcoordinates. The motion of the electron image past the scanning apertureresults in progressively selecting elemental areas of the image. Due tothe bombardment of the first multiplier plate of the electron multiplier24 by the electrons from different portions of cathode 2I in successionan image current is set up in the circuit including lead 95 connected tocollector grid I23, the terminating impedance element 36 and ground.This image current may be amplified by the vacuumtube amplifier 3'I, ifdesired, and transmitted over a suitable medium such as the balancedline 38. If desired, of course, the output of the dissector tube may beutilized, with or without further amplification, to modulate a carriercurrent for transmission over a suitable line or by radio. In accordancewith well-known television practice, moreover, synchronizing impulsesmay be combined with the image signaling current before transmission.

A 13,230 cycle saw-toothed wave is supplied for example, the well-knownarrangement for charging a condenser at a constant rate through theanode circuit of a vacuum tube and a gasfllled or vacuum tubearrangement for quickly discharging the condenser at regular intervalsunder control of steep wave front impulses. For this purpose there maybe employed the squaretop impulses of brief duration occurring at therate of 60 per second produced by the circuit comprising vacuum tubes40, 4 I, 42 and 43. The usual cathode heating batteries for thedischarge tubes of Figs. 3 and 4 are omitted from the drawings tosimplify the disclosure. Tubes and 4!, together with the associatedcircuit made up of resistors 44, 45, 46, 41, 49, condensers 49 and 50and anode battery 5| form a relaxation oscillator: multivibrator circuitwith its free fundamental frequency adjusted slightly below the cyclesynchronizong control frequency from source I! applied to the gridcathode circuit of tube 40. The condenser; 49 is charged by current frombattery 5| through a circuit including resistors 46, 45 and 48, and itis discharged, when the' grid of tube 40 becomes positive with respectto itscathode due to the potential of source II, through a circuitincluding the space current path of tube 49, resistor 48 and resistor45. While condenser 49 is being discharged, the grid of tube 4| is at anegative potential with respect to its cathode due to the potential dropacross resistors 48 and 45 and the condenser 59 is charged by-currentfrom battery through a circuit including resistors 41, 44 and 48. Whenthe discharge current of condenser 49 ceases to flow or is reduced to acritical value, the grid of tube 4| is no longer sufficiently negativewith respect to its cathode to prevent the flow of space current in tube4|, and the condenser 59 discharges through a circuit including. thespace current path of tube 4| and resistors 49 and 44. The input circuitof tube 4| is connected to the input circuit of tube 42, the grids beingdirectly connected, the cathode of tube 4| being grounded throughresistor 48 and the cathode of tube 42 being connected to ground throughthe grid biasing resistor 52 shunted by a condenser 53. The output oftube 42 is coupled to the input circuit of tube 43 through couplingcondenser 54 and input resistor 55. Space current is supplied to tubes42 and 43 by battery 58 shunted by condenser 51 through resistors 58 and59, respectively, the negative terminal of the battery being grounded.Grid biasing resistor 89 shunted by condenser 99 is in the leadconnecting the cathode of tube 43 to ground. The grid circuit of tube 42is over-biased (due to the potential drop across resistor 52) so thatsubstantially no anode current can flow except when the grid of tube 4|is driven positive while condenser 49 is being charged. During thesecharging periods of condenser 49 the grid of tube 42 becomes lessnegative (or it may become positive) with respect to its cathode tocause anode current to flow. As a result, the grid of tube 43 becomesmore negative and the anode current through resistor 59 is reduced. Dueto the discharging of condenser 49, a negative impulse is impressed uponthe grid of tube 42 and therefore a positive impulse upon the grid oftube 43. The tube 43 acts as a limiting amplifier being current limitedwhen tube 42 is non-conducting and driven to cut-off when tube 42 isconducting. Thus rectangular impulses of negative polarity are obtainedat the anode of tube 43 while condenser 49 is being discharged. Theseimpulses may be made of brief duratio by making the time constant of thecharging circuit of condenser 49 large compared with the time constantof the charging circuit for condenser 59.

Instead of using 60 cycle impulses to control the line sweep circuit 39,there may be employed preferably a stable oscillator of 26,460 cyclesfrom which is derived 13,230 cycle pulses, for directly controlling thehorizontal sweep circuit and from which may be derived 60 cyclesubharmonic current for controlling the speed of the film drive motorI8. This 60 cycle subharmonic current in this case would also be used inplace of the 60 cycle generator IT.

The apparatus for generating the sweep current to be supplied to thevertical deflecting coils 34 will now be described. The brief impulsesfrom the anode circuit of vacuum tube 43, occurring at the rate of 69per second, are impressed upon the input circuits of broad band vacuumtube amplifiers 8|, 82, 63 Fig. 4) through coupling condensers 84, 85,88, respectively, and input resistors 81, 89 and 89, respectively. Thereare provided for the amplifiers 8|, 92 and 83 the anode batteries II, I2and I3, re-

spectively, the anode resistors "14, I5 and I9,

-respectively, and grid biasing resistors 11, I8 and coupling condenser89 upon a sweep circuit 8| comprising condenser 82, constant currentvacuum tube 83 and gas-filled tube 84.

The condenser 82 is charged at a constant rate by current from source 85through the space current path of tube 83 and through variable resistor88, one plate of the condenser and the negative battery terminal beinggrounded. The charging rate and, therefore, the amplitude of thepotential to which condenser 82 is charged may be adjusted by changingthe setting of the variable resistor 88. A battery 81 is provided forbiasing the screen grid of tube 83 and the suppressor grid thereof isconnected directly to the cathode. The condenser 82 is dischargedperiodically under control of the 60 cycle impulses through a variableresistor 95, for adjusting the discharge rate, the space discharge pathof tube 84 and ground. The 60 cycle impulses are impressed upon thegrid-cathode circuit of tube 84 through a potentiometer 98 which isconnected in series with grid biasing battery 91. The positively chargedplate of condenser 82 is connected through condenser 88 to the grid ofphase inverter tube 89. Anode current supplied to this tube from battery99 through anode resistor 98 and grid biasing resistor 92, shunted bycondenser 93, the negative terminal of the battery being grounded. Aninput resistor 94 is connected between the grid of tube 89 and ground.The output circuit of tube 89 is connected through coupling condenser299 to the input circuit of mixer tube 9|. This tube is supplied withanode current from battery 29| through anode resistor 292 and gridbiasing resistor 293 which is shunted by a condenser 294. One terminalof input resistor 295 is connected to the grid of tube 9| and the otherterminal thereof to ground, the negative terminal of battery 29| alsobeing grounded. This branch circuit including tube 9| supplies a 60cycle saw-toothed wave component 2B of the complex vertical deflectionvoltage or current 2A in Fig. 2.

The 60 cycle rectangular impulses obtained from the output of vacuumtube 43 are also impressed upon a. multivibrator circuit comprisingvacuum tubes I99 and I9I for generating 12 cycle impulses. The circuitcomprises input condenser I92, input resistor I93 and anode resistor I94for tube I99 and input condenser I95, input resistor I98 and anoderesistor I9'I for tube |9|, anode current being supplied to both tubesfrom battery I98. The anode of tube |9| is coupled to the grid of tubeI99 through a condenser I99. The grid of tube |9| is connected throughcondensers 329 and 32| to the grids of tubes 9 and III, respectively,which produce 12 cycle sine waves, out of phase with respect ,to eachother. under control of the multivibrator output. The grids of tubes 9and III are also connected through grid leak resistors 322 and 323,respectively, to ground. Anode current is supplied to tube I I9 frombattery 2 through a circuit comprising an inductance element 3 shuntedby variable condenser||4 and grid biasing resistor II5 shunted bycondenser II8, while anode current for tube III is supplied from bazteryIII through a circuit comprising inductance element H8 shunted byvariable condenser H and grid biasing resistor I20 shunted by condenserI2I. The condensers I I4 and 0 may be adjusted to obtain the desiredphase relationship between the 12 cycle sine waves obtained from tubes 0and III.

The 12 cycle sine wave from the output of tube I I0 together with the 60cycle pulses from the output of tube 62 are impressed upon the input ofmixer tube I30 through coupling condensers I3I and I32, respectively,for producing 12 cycle impulses at the output of tube I30. The circuitof tube |30 comprises anode battery I33, anode resistor I34, gridbiasing resistor I35, grid condenser |36 and input resistor I31.

The output of mixer tube I30 is connected through condenser I80 to thesweep circuit |0| comprising condenser I82, constant current tube I03and gas-filled tube I84. The sweep circuit |8| is like the sweep circuit8| except for the circuit constants and there is produced at the outputof sweep circuit I8| a 12 cycle saw-toothed wave which is impressed uponthe input circuit of mixer tube |9| like the mixer tube 0|. The tube |9|is supplied with anode current from battery through resistor 202.

The 12 cycle sine wave from the output of tube I II and 60 cycleimpulses from the output of tube 03 are supplied to the input circuit ofmixer tube 230 through condensers 23| and 232, respectively. The circuitof tube 230 comprises anode battery 233, anode resistor 234, gridbiasing resistor 235, grid condenser 236 and input resistor 231.

The 12 cycle impulses from the output of tube 230 are impressed throughcondenser 200 upon the sweep circuit 20| comprising condenser 202,constant current tube 283 and gas-filled tube 284, this sweep circuitbeing like the sweep circuit I0 I The 12 cycle saw-toothed wave producedby the sweep circuit 28| is impressed upon the input circuit of mixertube 29| like mixer tubes 0| and I9I. The tube 29I, like tubes 9| andIOI, is supplied with anode current from battery 20| through resistor202.

The current from battery 20| flowing through resistor 202 flows throughthe space discharge paths of vacuum tubes 9|, |9| and 20I and thiscurrent varies in accordance with the potentials impressed upon thegrid-cathode circuits of these tubes. Therefore, the electromotive forcemeasured between ground and the anodes of tubes 0|, |9I and 20| whichare connected together has a complex or irregular saw-toothed wave formhaving as components a 60 cycle saw-toothed wave 23, from the circuit oftube 9| and two 12 cycle saw-toothed waves, 20 and 2D, out of phase withrespect to each other, from the circuits of tubes |9| and 29I,respectively. This irregular sawtoothed wave is impressed upon the inputcircuit of amplifier tube 300 through coupling condenser 30| across theinput resistor 302. Anode current is supplied to tube 300 from battery303 through anode resistor 304, grid biasing resistor 305,

when no varying electromotive force from mixer tubes 0|, I0| and 20I isimpressed upon the gridcathode circuit of tube 300, the electromotiveforce impressed upon the deflecting coils 04 and the steady currentflowing through the coils will be zero or such a value that the cathoderay beam is in its central position, that is, so that the electrons fromthe central portion of the cathode impinge upon the scanning aperture26. when an alternating saw-toothed wave 2A is then impressed upon theinput circuit of tube 000 the cathode ray beam will be deflected alongits vertical coordinate in such a way that the pictures of the motionpicture film are scanned as described in connection with Fig. 1.

Referring again to the curves of Fig. 2. curve 2A shows the irregularsaw-toothed wave which. is applied to the input circuit of tube 300 andto the vertical deflecting coils 04 of the image dissecting tube andthis curve also depicts the alternating portion of the current frombattery 20| flowing through resistive element 202 which is in serieswith the space current paths of vacuum tubes 0|, I0| and 20I, the phasereversals occurring in the circuit being not considered. Therefore, thecurve 2A represents the sum of the alternating portions of the currentsflowing in the space discharge paths of tubes 0|, IOI and 20 The threecomponents of the current represented by curve 2A are shown in curves2B, 2C and 2D, the curve 23 showing the 60 cycle sawtoothed wavecomponent flowing through tube 0| and curves 2C and 2D showing the 12cycle saw-toothed wave components flowing through tubes |0| and 20I,respectively. It will be noted that curve 23 has a gradually risingportion followed by. a more rapid falling portion, while curves 2C andCD each has a gradual falling portion followed by a more rapid risingportion. It will also be noted that while curves 2C and 2D have the sameamplitude, the amplitude of curve 23 is made somewhat less than that ofcurves 2C and 2D in order to avoid scanning the picture frame lines.These relative amplitudes can be controlled as desired by adjusting thevariable resistor of sweep circuit 0| and the corresponding resistors ofsweep circuits III and 20I. If desired, the amplitude of the 60 cyclesaw-toothed component 23 maybe further decreased at times for thepurpose of producing an image current representative of an enlargementor close-up of a portion of a picture or of portions of pictures. If,for example, curve 23 is decreased to about two-fifths of its normalamplitude, only the lower two-fifths of each frame will be scanned andthe reproduced image will be magnifled 2% times. In thus changing themagnification at the receiver it will be desirable, of course, to changealso the length of the horizontal sweep at the transmitter at the sametime in order to maintain proper picture proportions. It is also possi-.ble, if desired, to scan a picture while the fllm is stationary byshutting'off or reducing to zero the components 20 and 2D obtained fromthe circuits including tubes |0| and 20I, respectively, and controllingthe vertical deflection of the cathode ray beam only by the 60 cyclesawtoothed component 23.

Instead of combining a 60 cycle saw-toothed component and twoout-of-phase 12 cycle sawtoothed components for producing the verticaldeflecting wave, three 12 cycle out-of-phase sawtoothed components 613,0C and 6D may becombined as shown in Fig. 6 to'givegthe resultant wave6A. Obviously the resultant desired wave may be analyzed into stillother components, if

desired, some of which are square-topped wave components, for example,and these components may be combined to give the desired vertical sweepwave.

The method of generating the two 12 cycle saw-toothed wave components 2Cand ID by means of the apparatus shown in Fig. 4, will now be described,reference being made to the curves of Fig. 7. Curve IA shows the 60cycle impulses which are applied to the input circuits of tubes 6|, 62and 63 and to the multivibrator circuit I00, IOI. These impulses areimpressed directly upon the circuit including the sweep circuit 8| toproduce 60 cycle saw-toothed wave component IB. These 60 cycle impulsesare also superposed upon the 12 cycle sine wave obtained from the tunedcircuit I I3, H4 at the input circuit of tube I30. It will be notedthat, during each cycle of the sine wave, one of the impulses IDCsuperposed upon the sine wave is at a higher amplitude than theremaining impulses. This maximum impulse causes the space discharge pathof gas-filled tube I84 in sweep circuit IBI to break down, thus causingthe sweep condenser I82 to discharge. There is thus produced by thecircuit I ill the saw-toothed wave component, similar to IE but oppositein phase, having a portion of rapidly decreasing amplitude occurring atthe time that the impulse IOC occurs. Similarly the 60 cycle impulsesare superposed upon the 12 cycle sine wave from tuned circuit I I8, I ISin the input circuit of tube 230 to produce the wave ID having animpulse IOD at a predominant amplitude occurring ,5 second later thanthe impulse IDC, and the impulses IIID control the generation by sweepcircuit 2 of a saw-toothed wave component similarto IF but opposite inphase. The 12 cycle waves produced by the sweep circuits I8I and HI arereversed in phase by thetubes IIQI and 2!, respectively, to produce thewave components IE and IF, respectively.

When magnetic beam deflecting coils are used, as shown in Figs. 3 and 5,it is sometimes advantageous to make the sweep voltage impressed uponthe final amplifier 300 overshoot somewhat at the points of a suddenchange of amplitude of the saw-toothed wave 2A in order to counteractthe tendency for the sweep coils to set up transients at these points.This may be accomplished as illustrated by the curves of Fig. 8 bypassing wave 3A (like 2A) through a conventional pulse generatingcircuit to produce the impulse wave 83, the amplitude of which varies inaccordance with the rate of change of amplitude of wave 8A. The impulsesof wave 83, after being passed through a limiting amplifier to limit theamplitude to the values shown by the dash line, may be added in properphase to the wave 8A to obtain the voltage wave 80 to be impressed uponthe input circuit of the final amplifier 300.

' If desired, of course, a cathode ray light producing tube togetherwith a light sensitive device -may be employed for scanning the motionpicture film instead of the image dissector tube shown in Fig. 3. Fig.shows such a modification of the arrangement shown to the right of line5-5 of Fig. 3. In Fig. 5 the cathode ray tube 350 having a cathode 35Ianode 352, auxiliary anodes 351 and 353, horizontal deflecting coils353, vertical deflecting coils 354, and a coating 355 of fluorescentmaterial produces a spot of light for illuminating the film an elementalarea at a time. As the film II is moved continuously at a constant ratethrough the film frame l5, light from the cathode ray tube 353 iocussedupon the film I I by lens 20 illuminates different elemental areasthereof in succession. Light from the illuminated elemental areas isfocussed by lens I9 upon a light sensitive electric device, for example,a photoelectric cell 355, although a light sensitive electron multipliercould be used, and the image current produced by the device 356 isamplified by amplifier 31 and thence transmitted over line 38. Thecathode ray beam produced in tube 350 is deflected along horizontal andvertical coordinates in a similar manner to that in which the cathoderay beam produced in tube 22, Fig. 3,

- is deflected. For this purpose the usual sawtoothed horizontaldeflection voltage from source 39 is applied to the horizontaldeflecting coils 353 and an irregular saw-toothed current as shown inFig. 2A is applied from leads 3I0, 3 to the vertical deflecting coils354.

The elemental areas of the film III are scanned in succession in themanner described in connection with Fig. 1 whether the film is scannedby illuminating an elemental area of the film at a time, as in Fig. 5,or the film is scanned by means of an image dissector tube shown in Fig.3. It will be noted, however, that in Fig. 3 the image projected uponthe cathode 2| and, therefore, the electron image produced in the planeof aperture 25, is inverted with respect to the picture on the film andthat as the film moves down, as viewed in the figure, the image on thecathode 2| and the electron image move up. If no vertical deflectingcurrent, such as shown by curve 2A, were applied to the coils 34 of thedissector tube, the electron image would move up through a distance ofabout 3% frame with respect to the stationary aperture 25 in a fieldscanning period of ,4, second. However, the deflecting current appliedto the coils 34 causes the electron beam to be moved up an additionalframe distance, thus causing the electron image to move up a totaldistance of one frame during a frame scanning period.

What is claimed is:

l. The method of scanning motion picture film with an electronic devicecomprising continuously moving the motion picture film at asubstantially uniform rate, repeatedly deflecting the electron beamproduced in said device along one coordinate of motion at asubstantially uniform rate in one direction for effecting scanning alonga linear path and more rapidly in the opp'osite direction for returningthe electron beam between successive line scannings and repeatedlydeflecting the electron beam along a second coordinate of motionsubstantially perpendicular to the first coordinate in one direction forefiecting scanning of different linear elements in succession of pictureportions of the film, more rapidly deflecting the beam in the samedirection while the beam is traversing portions of the films betweensuccessive picture portions, and at intervals deflecting the cathodebeam in the direction opposite to the direction of the scanningdeflections for returning the cathode beam to a position for startingthe scanning of a picture portion.

2. The method of scanning motion picture film with an electronic devicecomprising continuously moving the motion picture film at asubstantially uniform rate, repeatedly deflecting the electron beamproduced in said device along one coordinate of motion at asubstantially uniform rate successive line scannings, repeatedlydeflecting the electron beam along a second coordinate of motionsubstantially perpendicular to the first coordinate in one direction foreifecting scanning of different linear elements in succession and morerapidly in the opposite direction for returning the electron beambetween successive scanning deflections along said second coordinate,the scanning deflections along said second coordinate being non-uniformin duration and in extent, and changing the deflection rate of saidelectron beam along said second coordinate during some of the scanningdeflections.

3. The method of scanning motion picture film which comprisescontinuously moving the film at a substantially constant rate,deflecting a cathode ray beam for scanning said film while in motion,generating at least four electrical waves of regular saw-toothed waveform and utilizing all of said waves to produce a wave of irregularsawtoothed wave form for controlling the deflection of said cathode raybeam.

4. The method of scanning motion picture film which comprisescontinuously moving the film at a substantially constant rate,deflecting a cathode ray beam for scanning said film while in motion,generating a plurality of electric waves of saw-toothed form, at leasttwo of said waves having the same frequency but being displaced in phaseby an amount to cause the peaks of one of the waves to be displaced intime with respect to the peaks of the other of said waves and utilizingall of said waves to produce a wave of irregular saw-toothed wave formfor controlling the deflection of said cathode ray beam.

5. The method of scanning motion picture film which comprisescontinuously moving the film at a substantially constant rate,deflecting a cathode ray beam for scanning said film and generatingthree electrical waves of saw-toothed wave form for controlling thedeflection of the cathode ray beam along a coordinate substantiallyparallel to the direction of motion of said film, two of said wavesbeing of the same frequency but displaced in phase by an amount to causethe peaks of said waves to be displaced in time and a third wave beingof a different frequency, the wave or waves of one frequency beingcharacterized by a relatively slow increase in amplitude followed by anabrupt decrease in amplitude and the wave or waves of the otherfrequency being characterized by a relatively slow decrease in amplitudefollowed by an abrupt increase in amplitude.

6. The method of scanning motion picture film which comprises moving thefilm continuously at a uniform rate, deflecting a cathode ray beam inone direction along a coordinate parallel to the direction of motion ofthe film at a certain rate during periods of scanning successive pictureportions of the film, and deflecting the beam in the same direction atan increased rate during a period between said picture scanning periods.

7. In combination, a source of electric impulses which recur at acertain frequency, means under control of said impulses for producing afirst regular saw-tooth wave of said frequency, means under control ofsaid impulses for producing a second regular saw-toothed wave of afrequency which is a submultiple of said firstmentioned frequency, meansfor producing a third regular saw-toothed wave like said secondsaw-toothed wave but out of phase with respect thereto, and means formixing said three sawtoothed waves for producing an irregular sawtoothedwave.

8. In combination, a source of electric impulses recurring at a certainfrequency, a second source and a third source of electric impulses whichrecur at a frequency which is a submultiple of said first frequency andwhich are out of phase with respect to each other, a plurality of meansunder control of said sources of impulses, respectively, for generatingcorresponding regular saw-toothed electric waves, and means forcombining said saw-toothed waves to produce a desired resultantirregular saw-toothed electric wave.

9. In combination, means for generating three electric waves of regularsaw-toothed wave form, means for reversing the phase of one of saidwaves with respect to the others of said waves and means for combiningthe wave of reversed phase with the others of said waves to produce anelectric wave of irregular saw-toothed wave form.

10. In combination, means for generating an electric wave of regularsaw-toothed wave form having a certain fundamental frequency, means forgenerating a second and a third electric wave of regular saw-toothedwave form having a different fundamental frequency, the wave or waves ofone frequency being characterized by a rate of change of amplitude withrespect to time which is positive and of relatively low value over aportion of a cycle and which is negative and of relatively high valueover the remainder of the cycle and the wave or waves of the otherfrequency being characterized by a rate of change of amplitude withrespect to time which is negative and of relatively low value over aportion of a cycle and which is positive and of relatively high valueover the remainder of the cycle, and means for combining said threewaves to produce a desired resultant wave of irregular saw-toothed waveform.

11. A combination in accordance with claim 10 in which the twosaw-toothed waves having the same frequency are out of phase withrespect to each other and of equal amplitude.

12. Motion picture film scanning apparatus for television transmissioncomprising means for moving the film continuously at a uniform rate,means for generating a cathode ray beam for scanning the pictures whilethe film is in motion, horizontal deflecting means for deflecting thecathode ray beam along a coordinate substantially perpendicular to thedirection of motion of the film, vertical deflecting means fordeflecting the cathode ray beam along a coordinate substantiallyparallel to the direction of motion of the film, a source ofsubstantially constant frequency alternating current for controllingsaid film moving means, means under control of said alternating currentsource for producing a high frequency substantially saw-toothed wave thefundamental frequency of which is a multiple of the frequency of saidsource for controlling said horizontal deflecting means, means undercontrol of said alternating current source for generating three lowfrequency substantially sawtoothed waves each having a fundamentalfrequency which is a submultiple of the fundamental frequency of saidhigh frequency saw-toothed wave, means for varying the amplitude of eachof said relatively low frequency saw-toothed waves, means under controlof said three relatively low frequency saw-toothed waves for producing acomposite wave having said three relatively low frequency saw-toothedwave components, and means for applying said composite wave to saidvertical deflecting means, thereby causing alternate picture frames tobe scanned an even plurality of times and the remaining picture framesto be scanned an odd plurality oi! times.

13. Motion picture film scanning apparatus for television transmissioncomprising means for moving the film continuously at a uniform rate,means for generating a cathode ray beam for scanning the pictures whilethe film is in motion, means for deflecting the cathode ray beam along acoordinate substantially perpendicular to the direction of motion of thefilm, means for generating three substantially saw-toothed electricwaves, means for varying the amplitude of each of said waves, means forproducing a composite electric wave of irregular saw-toothed wave formhaving said three saw-toothed wave components, and means controlled bysaid composite wave for deflecting said cathode ray beam along acoordinate substantially parallel to the direction of motion of thefilm,

14. Motion picture film scanning apparatus for television transmissioncomprising a source of substantially constant frequency alternatingcurrent, means under control of said alternating current source formoving the film continuously at a uniform rate, means for generating acathode ray beam for scanning the pictures recorded on the film whilethe film is in motion, means under control of said alternating currentsource for deflecting the cathode ray beam along a coordinatesubstantially perpendicular to the direction of motion of the film,means under control of saidalternating current source for generatingthree substantially saw-toothed electric waves, means for varying theamplitude of each of said waves, means for producing a compositeelectric wave of irregular saw-toothed wave form having said threesaw-toothed wave components, and means controlled by said composite wavefor deflecting said cathode ray beam along a coordinate substantiallyparallel to the direction of motion of the film.

15. The method of scanning motion picture film with a cathode ray beamscanning device having means for deflecting the beam, which comprisesmoving the film continuously at a uniform rate, generating and applyingto said deflecting means a first electric wave for deflecting the beamin a direction transverse to the direction of motion of the film, andgenerating and applying to said deflecting means a second electric waveportions of which have a certain slope to cause the deflection of thebeam in a direction parallel to the direction of motion of the filmduring the periods of scanning successive pictures recorded on the filmand other portions of which wave have a different slope for positioningthe beam for commencing the scanning of a picture, each of said otherportions having a slope greater than, and in the same sense as, saidfirst mentioned slope for reducing the time elapsing between thecompletion of the scanning of a picture and commencement of scanning ofan adjacent picture.

16. The method of scanning motion picture film with a cathode ray beamscanning device having beam deflecting means, which comprises moving thefilm continuously at a uniform rate, generating and applying to saiddeflecting means a first electric wave for deflecting the beam in adirection transverse to the direction of motion of the film to scan thefilm in parallel elemental strips, and generating and applying to saiddeflecting means a second wave comprising recurrent scanning portions ofequal duration each having a slope to deflect the beam in a directionparallel to the direction of motion of the film whereby said slope andthe speed of said film determine the period of scanning a picture, eachof certain of said scanning portions of said wave being followed by aportion of much' shorter duration and of much greater and reverse slopeto position the beam for commencing another field scanning of thepicture a scanning of which has just been completed under control of thepreceding scanning portion with an offset from the preceding fieldscanning in the direction in which each of said elemental strips isscanned whereby interlacing of the field scannings of the same pictureis effected, and each of the remaining ones of said scanning portions ofsaid wave being followed by a portion having said short duration and aslope intermediate said two first mentioned slopes and in the same senseas the said first slope for positioning the beam for commencing thescanning of a succeeding picture portion.

AXEL G. JENSEN.

